Negative impedance device



Oct. 9,-1928. v v 1,687,253 M. LATOUR NEGATIVE IMPEDANCE DEVICE FiledNov. 20, 1923 Suva/.4 60:

MARI US LATOUR Patented Oct. 9, 1 928.

UNITED STATES MARIUS LATOUR, OE PARIS, FRANCE, ASSIGNOR TO LATOURCORPORATION, OF "JERSEY 1,687,253 PATENT OFFICE.

CITY, NEW JERSEY, A CORPORATION OF DELAWARE.

NEGATIVE IMPEDANCE DEVICE.

Application filed November 20, 1928, Serial No. 675,838, and in FranceDecember 5, 1922.

This invention relates to improvements in arrangements for producingnegative impedance, and has for its purpose the produc-' tion ofnegative impedance which may be interposed in a telephone line in orderto counterbalance the impedance of the line and reduce the attenuation,but it-will be understood that this invention is not limited to the usejust indicated.

Various specific features of the invention will appear from the detaileddescription and appended claims.

yinvention is illustrated in the accompanying drawing, in which v Fig.1shows one form of my invention as embodied in a resistance-coupledamplifier;

Fig.2 shows an arrangement according to mydinventipn utiliz'ingtransformer coupling;

F-igsa3 and 4 show arrangements of apparatus adapted to'be inserted in atelephone line to reduce attem1ationand prevent distortion. T v v InFig. 1 there are shown two three-electrode vacuum tubes 1 and 2, eachhaving a plate, a filament and a grid with circuits arranged toconstitute a two-stage resistancecoupled amplifier. The plate circuit ofvacuum tube 1 is energized by the combined voltagesof batteries 3 and 5through resistance 12. The voltage of battery 5 is such that it normallycompensates for the resistance drop of the plate voltage in resistance12 in such a manner that the voltage between points 10 and 11 isnormally equal to zero. In the same .way,the plate circuit of vacuumtube 2 is energized by the sum of the two voltages of "the batteries 4and 6 through resistancelfi, the voltage of battery 6 being such thatthe resultant voltage between terminals 13- and 141' is'normally zero.An impedance 9 having a value a is shunted between the grid and filamentof vacuum tube 1 between the terminals 7 and 8.

From Fig. 1 it will be noted that there is a circuit including thevarious terminals 7, 8, 11, 14 and 13-andif we consider that a currentflows in this circuit through the impedance9 which has a value a, itwill be understood that the passage of current develops a voltage 1%between the grid and filament of vacuum tube 1 and this voltageamplified successively by the two vacuum tubes 1 and 2 results, inaccordance with the usual characteristicofvacuum tubes, as a negativeohmiedrop between the points 14: and 13 of the resistance 15. It,therefore, results that for a suitable value of imped- -ance 9 having aresistance, an inductive reactance, and capitance, there is obtainedbetween terminals 7 and 13 a negative im edance depending on thecharacteristics 0 the clrcuits.

In order to obtain a negative impedance of a sign exactly opposite tothat of the impedance 9, which is connected in shunt to the grid andfilament of the first vacuum tube 1, it is necessary to place in serieswith the Impedance -9 a certain resistance 16 which, transformed into anegative resistance by the operation of the amplifying system, serves.to counterbalance the effect of the positive resistance'connected inthe late circuit of the'second vacuum tube 2.

he resistance 16 is substantially equal to v the resistance 15.

According to this invention, we may emplo instead of direct coupling byresistance, coupling by transformers 17 and 18 as shown in Fig. 2 inwhich the same reference characters indicate the same parts as inFig. 1. In this case an even number of tubes is no longer necessary. Itis sufficient to take a convenient sense of circulation of the windingsof the transformers interposed in the work circuit and the number oftubes may be anything. If it is supposed that we have to do with aperfect type of transformer (magnetizing current zero, capacity ofwindings zero, leakage zero, losses zero), the operation will be thatshown in Fig. 1. In practice it should be arranged that transformers 17and 18 approach the perfect type of transformer with theorder ofmagnitude of the frequencies considered. The

magnetizing current. may be compensated by a capacity in shunt. Thesetransformers may be without iron in the case of very high frequencies.The input transformer, on the other hand, may be arranged with a ratioof transformation sufliciently low so as not to cause in the gridfilament circuit a resultant eifect capable of disturbing the desiredoperation. The resistance 15 may be variable; it may be represented bythe winding connected to the plate and represented even by the losses inthe iron of the transformer.

Fig. 3 shows an arrangement in which the real impedance .2 is a cable orartificial line equivalent to a real cable or real line in a responds toa cable or artificial line of inverse constants, as compared with Fig.3, (capacities in series and inductances in shunt in such a manner thatthe negative impe ance obtained may permit not only the reduction of theattenuation, but prevent distortion. In a general way, the realimpedance 9 may be constituted by all elements appro riately selected,inductances, capacities an resistances combined in any manner torepresent a suitable artificial line.

In order to satisfy symmetry, we may arrange two amplifier systems for asingle line. In the first system t on the north side and the platecircuit on the south side; While in the second system the grid circuitwill be on the south side and the plate circuit on the north afterthemanner of the well known one-way repeater. The real impedance 9 mayalso be, for example, the modulation circuit of a magnetic amplifier orof a frequency multiplier, the excitation circuit of a high frequencyalternator and in a general way any circuit resenting a reactance whichis a function 0 the frequency. The distortion suffered by telephoniccurrent in traversing such a circuit e grid circuit may be may then beprevented by roviding on the plate side a negative impedance of a valveequivalent to that shunted about the grid side in such a way that thewhole represents only a residual impedance corresponding to a pure ohmicresistance.

Having described my invention, what I claim is:

1. In apparatus for producing a negative impedance, a vacuum tubeamplifier comprising an anode, a cathode and a control electrode, animpedance connected in circuit between said cathode and said controlelectrode, a transformer having its windings inative impedance, thecombination of a vacuum tube amplifier having an anode, a cathode and acontrol electrode, an input circuit comprising an impedance having aresistance associated therewith, an output circuit comprising aresistance, a transformer having its primary shunting said impedance,and its secondary connected in the control circuit of said amplifier,and a second transformer having its primary winding in the anode-cathodecircuit of said amplifier and its secondary winding shunting theresistance in said output circuit.

MARIUS LATOUR.

